This invention relates to an optical recording medium for making optical read and write of information by using an organic dye.
Photochromic compounds are known as a material which undergoes a reversible change of color upon exposure to two types of light source differing in wavelength. Typical examples of such photochromic compounds are spiropiran and fulgides. Application of these compounds to the optical recording media for binary memory by making use of said reversibility of the compounds has been proposed, but no successful attainment of their practical application is yet reported.
There are several problems in utilization of photochromic materials for an optical recording medium. One important problem is the unstability of the colored form (colorless form in the case of inverse photochromic material). Most of the known photochromic materials are poor in stability of colored form; the colored form returns to the colorless form when placed in a dark place. Therefore, when using such photochromic materials, it has been impossible to store the recorded information, and thus the use of such materials has been limited to the temporary memory type optical recording media.
Another important problem is the method for forming a thin film from said photochromic materials. The Langmuir-Blodgett method is an excellent technique for forming a uniform thin film. It has been however difficult to make a thin film from said materials by the Langmuir-Blodgett method because most of the known photochromic materials had a molecular structure with weak hydrophobicity.